This invention concerns artificial devices for implantation in the human body. More particularly, it concerns a prosthetic articulating joint.
The use of artificial devices implanted in the human body for replacing defective, damaged or diseased anatomical structures has long been known.
One form of such prosthetic devices replaces anatomical joints of the body having ball-and-socket characteristics such as, for example, the hip joint. This hip prosthesis essentially provides a detachable interconnection between the femur and acetabulum socket of the pelvis to accomplish the universal type movement associated with the replaced natural biological joint. Conventional prosthetic total hip joints normally comprise an acetabulum type cup member with a spherical cavity, which may be suitably secured in a variety of ways to the acetabulum socket of the pelvis, and an artificial femoral insert, which is appropriately attached to the femur. The femoral insert includes a smooth and substantially spherical head member which mates with, and is rotatably supported by, the spherical cavity of the cup member. As a result of this structural interrelationship, a ball-and-socket type joint is created which permits the ordinary type of articulated motion associated with the human hip joint.
Among the several known concepts for providing artificial articulated joints are prostheses utilizing bicentric action, such as those of U.S. Pat. No. 3,813,699 and 3,863,273 directed primarily to hip joints in which articulation can occur both between the head of the femoral insert and the cup member of the prosthesis and between the prosthesis and the acetabulum socket of the pelvis. While both of these prostheses are bicentric and embrace the concept of wear between plastic and metal rather than between metal and bone, neither device provides means whereby the head of the femoral insert is more easily inserted into than withdrawn from the spherical cavity of the acetabulum cup member so that the prosthesis is not subject to joint dislocation. Such means are provided in the prosthesis of U.S. Pat. No. 4,044,403. This prosthesis, however, in turn does not provide means for more suitably encasing the plastic cup member in its metallic outer shell.
It is therefore a primary objective of the present invention to provide a means whereby the plastic cup member of a bicentric joint prosthesis is easily inserted into and effectively retained by its metallic outer shell.